The present invention relates to improvements in a rolling bearing, and more particularly to the rolling bearing for an automotive power train, which is used to support a power transmitting part such as a gear, a shaft, and a pulley in an automotive power train, for example, in a transmission, used to support a power transmitting part in a belt-type continuously variable transmission serving as an automotive power train, and suitably used for peripheral auxiliary equipment for an automotive power train such as a grease-filled bearing used for an alternator, electromagnetic clutch, idler pulley, etc. and the rolling bearing used for a fuel injection pump. The rolling bearing is also suitably used for a compressor, for exaemple, of an air conditioner, which is operated under a lubricating condition in which hydrofluorocarbon as a refrigerant and a lubricant dissolvable in the hydrofluororcarbon are mixed.
In recent years, a power train used for a motor vehicle or the like has been required to be small in size and light in weight to improve fuel efficiency and increase the power. Accordingly, a rolling/sliding member such as a rolling bearing, gear, and the like used for a power train is forced to be operated in a severe environment such as high load and high rotational speed, in addition to the requirement for being small in size and light in weight.
For example, in the case of a grease-filled bearing used for an alternator, electromagnetic clutch, and the like, not only it is required to be small in size and light in weight, but also it is used in a severe environment such as high load, high rotational speed, and high vibration. As a result, as described in NTN Technical Review No. 61 and NSK Technical Journal No. 656, there is a report that the grease-filled bearing separates in a short life due to a change in structure of peculiar mode in the rolling surface.
As described in NTN Technical Review No. 61, the cause for this short-life flaking is thought to be that the use in a severe environment such as high load, high rotation, and high vibration causes so-called mirror-surface wear of rolling surface, the formation of new metal surface caused by this wear plays a catalytic role to decompose grease or entering water, and hydrogen generated at this time intrudes into steel, which results in flaking due to hydrogen enbrittlement.
It is thought that at this time, the hydrogen embrittlement flaking in the rolling surface is caused through (1) a step in which a hydrogen atom or ion is generated by the decomposition of hydrocarbon or entering water→(2) a step in which the generated hydrogen atom or ion intrudes into steel→(3) a step in which the material is embrittled by the intruding hydrogen.
Conventionally, as measures against the above-described short-life flaking due to hydrogen embrittlement, measures in which triiron tetroxide is formed on the rolling surface by black oxide finishing (as disclosed in Japanese Patent Provisional Publication No. 2-190615), measures in which a lubricant containing a deactivator is used to reform the rolling surface so that the reaction of deactivator is accelerated (as disclosed in Japanese Patent Provisional Publication No. 2001-20958), and measures in which the content of Cr of base material is increased to form an inert oxide film such as FeCrO4 on the surface (as disclosed in Japanese Patent Provisional Publication No. 8-177864) have been taken.
In these measures, the inert oxide film is formed on the rolling surface, and thus catalytic action due to the formation of new surface is restrained, by which the decomposition reaction of hydrocarbon or entering water is made less liable to occur to reduce the amount of generated hydrogen, that is, the aforementioned hydrogen generating step (1) is improved. However, since the catalytic action against the decomposition reaction of hydrocarbon exists not only on the new surface but also in acid etc. yielded by the decomposition of entering water and an additive, the generation of hydrogen cannot be restrained completely by only the inert film depending on the lubrication environment, and it is difficult to prevent the generated hydrogen from intruding into steel.
Also, a conventional technique in which Al, Nb, N, etc. are added to steel to make the austenitic crystal grain fine, by which a metal structure invulnerable to hydrogen embrittlement has been disclosed in Japanese Patent Provisional Publication No. 5-255809.
In this technique, the resistance to hydrogen embrittlement of the material is increased by finer crystal grain, that is, the aforementioned material embrittlement step (3) is improved. However, finer crystal grain increases the area ratio of crystal grain boundary, which is a hydrogen intruding passage, so that the amount of hydrogen intruding into steel sometimes increase.
Therefore, a rolling member and a sliding member that can restrain the short-life flaking due to hydrogen embrittlement must be provided by improving the aforementioned hydrogen intruding process (2), which has not been improved by the conventional technique, that is, by surely restraining the intrusion of hydrogen into steel even if the amount of generated hydrogen is increased by a change in service environment or lubrication environment.